To prevent flooding, hardstandings must be sloped to permeable ground. This means they should be made of pervious materials such as clay bricks and concrete blocks that allow water to pass through voids and joints. This will reduce the impact on the environment and help save money on drainage. In addition, hardstandings must not run onto the road.
1.5% – 2%
When designing drainage systems, slope is vital. A slope of more than two percent is too steep, and the water will not flow freely. This can lead to clogging and other problems. Therefore, the slope of the drainage pipe should be at least one and a half percent.
When paving a driveway or landscaped area, a one-percent slope is recommended. But if the area is landscaped, a slope of two percent is ideal. The slope should be consistent from foot to foot. For small and medium sized drains, the minimum slope is one and a half inches per 12 feet, while larger drains should be one and a half inches per foot. In addition, all drain pipe should slope downhill at least one-tenth inch for each three inches.
Backfall in a drain
Surface water drains from buildings need to be at least 0.3 metres steeper than the slope of the land around them. There are also different types of drain, including longfall and crossfall. Longfall is the type of drainage where water and sewage are trapped at a low point.
Surface water drainage from hardstandings must be designed to slope towards a permeable area. Suitable materials include porous concrete, asphalt, and clay bricks. Porous materials are preferable as they allow water to drain through the joints and voids and thus minimise the impact on the environment. This is important because surface water from hardstandings can end up on the highway if they are not designed correctly.
In England, Wales, and Northern Ireland, surface water drainage must be approved by the Environment Agency. In Scotland and Northern Ireland, proposals should also be vetted by the River Purification Authority. The design should be suitable for the soil type, and the drainage must be sufficient to take the peak load. The BS EN 752 document provides guidance on drainage design.
Installation of underground drainage systems
The first step in the installation of an underground drainage system is to dig out a trench, usually 300mm wide, to lay the pipes. The trench should be lined with pea shingle or fine gravel to protect the pipes. The trench should also be fenced off to prevent young children from wandering in the trench. Once the trench is lined, the trench should be backfilled with 100mm of soil or pea shingle.
Underground drainage systems can be tricky to install without professional help, but with the right guidance and planning, the process can be simple and effective. Obtaining all of the necessary equipment and fittings for the installation can speed up the process.
Design of soakaways
A successful design of a soakaway must take into account the landscape and ecology of the site where the soakaway will be situated. Because of the potential for pollution of groundwater, discharges to the soakaway must be designed to minimize or mitigate their impact. The standard for designing a soakaway provides guidance for this purpose.
A successful soakaway design should be based on evidence rather than assumptions. The permeability of the ground should be determined in advance. This can be done by analysing the geology of the area. A BRD drainage surveyor can carry out a soakage test as part of a flood risk assessment to determine how permeable the soil is.
Design of septic tanks
The design of a septic tank depends on a few critical parameters. One of these is the amount of time the tank must be held in operation. In a small installation, the time period should be at least 24 hours. Similarly, for larger installations, it should be at least 36 hours. This is to ensure durability of the tank.
The walls of a septic tank should be between 50 and 100 mm thick. The wall thickness varies depending on the size of the tank. The top of the tank should be covered with an RCC slab. In large tanks, there are holes to allow the sludge to flow through. The tank should also have circular manholes of 500mm in diameter. Other features include rectangular openings of 600 X 450mm. The tank should also be ventilated using cast iron or asbestos pipes. The pipes should be located at least 2 m above ground level. In addition, it should have a mosquito proof wire mess or cowl to prevent insects from entering it.
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